Process of removing lead from copper base alloys



rRocEss or REMOVING LEAD FRoM cornea BASE ALLOYS Paul Kemp, Bois Colombes, France No Drawing. Application January 23, 1954 Serial No. 406,886

Claims. (Cl. 7512i The present invention relates to the process of removing lead from finely divided copper base alloys such as turnings and grindings.

. A purpose-of the invention is to remove lead from finely divided scrap of copper base alloys so as to permit the scrap to be remelted in order to produce ingots which are relatively low in lead.

QA further purpose is to eliminate lead from particles of copper base alloy by treatment with nitric acid as substantially the only reagent, thus minimizing the solution of copper and other ingredients, operating preferably at room temperature and in a concentration range of 2 to 13 percent of concentrated nitric acid in Water by volume.

A further purpose is to employ a counter current treatment of the particles of copper base alloy, first with weak nitric acid and then with stronger nitric acid.

A further purpose is to degrease the particles of copper base alloy, prior to treatment with the nitric acid.

A further purpose is to agitate the nitric acid and the copper base alloy particles during the treatment.

A further purpose is to recover the lead from the solution by precipitation.

Further purposes appear in the specification and in the claims.

The removal of undesirable elements from alloys is usually accomplished by fusion of the alloy, followed in some cases by oxidation or volatilization of elements to be eliminated. In other cases, fractional solidification is employedto eliminate undesired elements, which are concentrated in one of the fractions obtained. In still other T instances, substances areadded with which the base alloying material forms insoluble compounds. I

It is not always possible however to employ therma processes. Aluminum, zinc or iron can be removed from copper base alloys by one of these methods, but it is not possible at the present time to decrease the lead content even to a slight extent without at the same time losing a large part of the tin.

The elimination of lead from such alloys is, however, an important problem when it is considered that many specifications for bronzes of high quality permit very small lead contents. It has, therefore, in many cases been necessary to make such high quality bronzes from virgin copper and tin. The use of secondary bronze from scrap has not been permitted because such material has too high a content of lead. It is therefore necessary to find some other process to solve this problem.

Metallic alloys are essentially composed of metallic crystals, solid solutions and intermetallic compounds. The differences between these various constituents are readily recognizable under the microscope. It is thus theoretically possible to eliminate a certain constituent by a wet process, treating the alloy with a reagent which is capable of dissolving the desired constituent without attacking the rest of the alloy.

Lead is of course practically insoluble in copper alloy in the solid state, and it appears as a distinct phase in aren t F 2 the micro-structure of bronze and brass. The elimination of lead by a wet process is then possible in alloys which are sufiiciently finely divided to be attacked in depth.

it has already been proposed to employ certain organic compounds such as tartarates or citric acid in combination with nitric acid to remove lead from grindings or turnings of bronze. This process has not been satisfactory, and in any case it is necessary to have an apparatus having a lining of special material and to operate at a temperature of about 100 C.

Lead has also been eliminated by double decomposition with salts of copper in acid solution. Such copper salts are relatively expensive. Copper deposits on the material under treatment in the course of the reaction and to a certain extent retards the penetration of the reacting materials into the interior.

In accordance with the presentinvention, lead is removed from copper alloys and particularly finely divided copper base alloys such as turnings and grindings of brass and bronze, by a reaction with nitric acid alone. l

Nitric acid is in the present process the only reactant. When one realizes that nitric acid not only attacks lead. but also attacks copper and zinc, and is used in analytical laboratories to dissolve bronze and brass, it will be appreciated that the use of nitric acid alone to dissolve lead from a copper base alloy is very remarkable. The present inventor has discovered that by observing certain precautions as indicated herein, it is possible to eliminate the lead without dissolving the slightest trace of copper.

The process of the present invention has the advantage that the price is low. Another great advantage of the present process is that operation is possible at ambient temperature and in fact is preferably carried on at such temperatures. Thus, a better result is obtained than by previous processes, using a very simple installation and at low cost.

The concentration of the acid to be employed depends in part upon the material to be treated. Generally speaking, good results have been obtained, using concentrations of from 2 to 13 percent of nitric acid in water by volume. Higher concentrations are preferably used at lower temperatures (below 20 C.) and lower concentrations are preferably used at higher temperatures such asare encountered in summer.

It is preferable to start out a deleading operation using an acid which has previously been used in'deleading an. earlier charge. The last residual'content'of lead is pref -J. erably eliminated by fresh and more concentrated nitric": acid.

Bronze turnings in practice almost always are coated with oil or grease. It has been found that the elimination of lead can be accomplished most effectively if the turnings have previously been subjected to a treatment which removes this grease coating suitably by heating above the point of decomposition of the grease, or by degreasing the turnings with a solvent.

in order to secure a rapid and complete reaction, it is desirable to mix the turnings intimately with the acid. A simple means of mixing is to carry out the process in a rotating drum containing the finely divided copper base alloy. The drum can be constructed of wood which is quite resistant to the treatment.

Depending upon the nature of the copper base alloy particles, the lead will be more or less completely removed. On the average to percent by weight of the lead content is eliminated when ordinary turnings of brass or bronze are used, and percent by weight is eliminated from grindings or very fine turnings.

To recover the lead, the solution containing the lead can be neutralized, for example by lime or by a carbonate, and the total quantity of lead is then recovered as a hydroxide or carbonate substantially free from other .7 2,825,644 p a r metals. The appropriate lead compound is easily reduced to metallic lead.

7 Example I .lQOO-kilograms of bronzeturnings of the following composition byweight: r

are charged into a rotating drum which is filled with a mixture of 640 liters of water and 60 liters of concentrated are treatediwith the leaded solution remaining from the treatment of Example I. Thetreatment with this solution is continued for30 minutes, and then the solution is emptied, at which time it contains 85 grams of lead per liter.- The drum is thenv charged with a new solution of i 4 i 160 kilograms of lead were recovered by precipitation'in the form of hydroxide. It will be evident that the process of the invention has wide application particularly in secondary copper refining nitric acid. The drum is turned for 90minutes at a temperature'of 1 8-C and the solution is then emptied. The solution when emptied'co'ntains 50 grams of lead per liter. The" t u nings after the treatment have the. following analysisby weight Percent Tin." "6.9 Copper '87.? Lead V 1.0 Zinc 4.2

The recovery from thetreatment amounts to 964 kilograms of alloy. V p

. a Example 11 .1000 kilograms of leaded bronze tnrnings of the followins a y s by weight;

- 1 Percent Tin V j 7.5 Copper 75.8

Lead 7 14.7,

' Zinc 1.8

640 liters'of water and 60 liters of nitric acid. This new solution is usedl to treat the turnings'with agitation in the drumior 'oneihour; after which. the. new solution is re- 7 moved and theturnings are dried. The recovery of turnings is 870 kilograms havingthe following composition byweight: v

From the two solutions obtained from this example,

especially to produce secondary ingots of precise analysis.

in view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the process shown, and I, therefore, claim all such insofar as they fallwithin the reasonable spirit and scope of my claims.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

l. The process of removing lead from finely divided copper base alloys, which comprises treating the particles of copper base alloy with a water solution of 2 to 13% of nitric acid by volume in which nitric acid is the only reagent present.

2.. The process of claim 1, in which the treatment is at ambient temperature.

7 3. Theprocess of claim 1, in which the. treatment is carried on first with partiallyspent nitric acid solution and then with a stronger concentration of nitric acid solution.

4. The process, of claim 1, in which the particles of copper base alloy, and the nitric acid during treatment.

5. The process of claim 1, in which the lead is subse-. quently recovered from the. solution'by precipitating as a salt of the class consisting of a hydroxide and a carbonate.

solution are. agitated References Cited 'inthe file of thisrpatent UNITED STATES PATENTS .l, 192 ,945 SherWo'od' Aug. 1, 1916' 1,051,683 France Sept. 16, 1953 OTHER REFERENCES American, Society for Metals; Cleveland, Ohio.' Page 

1. THE PROCESS OF REMOVING LEAD FROM FINELY DIVIDED COPPER BASE ALLOYS, WHICH COMPRISES TREATING THE PARTICLES OF COPPER BASE ALLOY WITH A WATER SOLUTION OF 2 TO 13% OF NITRIC ACID BY VOLUME IN WHICH NITRIC ACID IS THE ONLY REAGENT PRESENT. 